The way people’s voices change when they talk to babies – nature or nutty?
A global study in Nature Human Behaviour has found the way people speak to infants (using a higher or more variable pitch and exaggerating vowel sounds, and known as “parentese”) is a behaviour that’s consistent across cultures – but there are differences between nations.
The findings will be familiar to parents and people who have spent a lot of time around babies, says Cody Moser one of the paper’s lead authors and a PhD student at the University of California Merced.
Infant-directed speech is “higher than adult pitch, its vowels tend to be more exaggerated and variable than in adult speech”, he says. Infant-directed song shares some of these features but tends to be less ‘intense’. This could be because when parents talk to babies, they are often trying to get their attention, whereas they might sing to calm them down, Moser says.
The study encompassed recordings of 410 people from 21 different societies spanning six continents and 18 languages. It required a global effort involving more than 40 authors.
The societies ranged from cities with millions of people (such as Beijing, China), to smaller urban centres (like Wellington, New Zealand), through to small-scale hunter gatherer groups (like the Hadza people in Tanzania). They included varying degrees of isolation from media, including four places with no access to television, radio or internet.
The goal was to build a diverse sample of recorded societies, says cognitive scientist Courtney Hilton, a post-doctoral fellow at Harvard University and another of the paper’s lead authors.
“Much of the prior research on infant-directed vocalisations has been done in large-scale urban societies, and typically western societies. There are some exceptions, but on the whole, prior to our study, it was really unclear whether prior findings from these mostly western societies would generalise to others,” he says.
For each location, Moser’s team needed the same types of recordings from the people with babies, including four key items: “the speech they use when talking to a fussy infant, the song they use when trying to calm a fussy infant, the day-to-day speech they use with adults, and the songs they sing to/with other adults.”
“Human vocalising for infants seems to be strongly stereotyped across cultures, but these effects differ in magnitude across societies,” says Dr Samuel Mehr, the paper’s senior author and director of the Music Lab at Harvard University’s Department of Psychology.
Some cultures were more exaggerated.
Across the ditch, parents from Wellington, New Zealand really leaned into their baby talk, the study found.
“Wellington was actually the easiest one for listeners to predict whether or not a song/speech as infant-directed or adult-directed,” Moser says. Wellington parents had some of the most exaggerated features, in the way they altered their pitch or vowel sounds when talking to their infants.
Perhaps disappointingly for those looking to draw trans-Tasman comparisons, no Australian comparison cities or towns were included in the study.
Overall, 1,615 recordings captured people speaking or singing to babies or adults.
To classify and sort the recordings, researchers trained an Artificial Intelligence model.
Hilton says, “we trained the model in a way that wasn’t biased to any one of the 21 societies, in the end learning a ‘global fingerprint’ representing how much it valued certain acoustic features to make guesses about whether a recording was directed to a baby or not.”
The research also drew on citizen science, inviting more than 50,000 volunteers from 187 countries to listen to the recordings.
Listeners were played a recording and asked, “Who do you think they are singing or speaking to?” They could respond ‘adult’ or ‘baby’. You can even have a go at the Music Lab website.
The results showed that listeners can readily identify baby talk, even when the person is speaking or singing in a different language.
According to the study, baby talk is believed to serve a functional purpose, helping to soothe or interact with an infant and supporting language development.
Hilton says one of the things they are now looking into are the potential health benefits of parents singing to babies, like regulating a child’s emotions or meeting their social needs.
And, if you’re worried about sounding patronising by speaking in a higher pitch when talking to small humans? Don’t be. According to the paper, babies prefer baby talk.